For one semester I was in Stuttgart with Ewald who had given me really the basis for my thesis, and I was very happy there, happier than I had been for years, and so I was very reluctant to go back to Sommerfeld when Sommerfeld claimed me. But Sommerfeld gave me several inducements; one was the Habilitation and the other was that he would get me a travel fellowship from the Rockefeller Foundation, which he did. And he suggested that I go one semester to Cambridge, England, which was of course a big center, and the other semester to Rome, to Fermi who was a rising sun in theoretical physics. Fermi had published his Fermi's Statistics and then, as I already mentioned, he had done a very good presentation of quantum electrodynamics in momentum space which made it very much more readable than Heisenberg and Pauli who had done it in ordinary space. So I went to Cambridge and found it a very congenial place, in fact, I had been quite unhappy in Germany because most of the people around me in Germany were arch conservatives, they constantly talked about the terrible disgrace of the Versailles Treaty and were dissatisfied with life quite generally. In Cambridge I found people relaxed, talking about much more general and more interesting things, and I found in Cambridge I could make friends far more easily than I could in Munich. I had made friends during my high school time, but really no additional ones during my student time. So Cambridge was a great revelation that people could be human and I had a very good time there. I didn't do terribly much additional work, I did do some work. I had a wonderful professor to report to, Ralph Fowler, who had worked mainly in statistical mechanics but who was very happy to listen to me when I talked to him about energy levels in crystals and... and stopping power and all sorts of things. I talked to the experimentalists, Blackett and Cockcroft and Chadwick, and got very interested in experiments which I had not been in Munich. So Cambridge was a very good experience, and then Rome was an even better experience in some ways.

The late German-American physicist Hans Bethe once described himself as the H-bomb's midwife. He left Nazi Germany in 1933, after which he helped develop the first atomic bomb, won the Nobel Prize in Physics in 1967 for his contribution to the theory of nuclear reactions, advocated tighter controls over nuclear weapons and campaigned vigorously for the peaceful use of nuclear energy.

Silvan Sam Schweber is the Koret Professor of the History of Ideas and Professor of Physics at Brandeis University, and a Faculty Associate in the Department of the History of Science at Harvard University. He is the author of a history of the development of quantum electro mechanics, "QED and the men who made it", and has recently completed a biography of Hans Bethe and the history of nuclear weapons development, "In the Shadow of the Bomb: Oppenheimer, Bethe, and the Moral Responsibility of the Scientist" (Princeton University Press, 2000).